This invention relates to electronic computer systems, and, more particularly, to a backup computer power system that supplies power during main power source interruption and controls sequencing of the computer during the shutdown and restarting after such an interruption.
Electronic computers now play a central role in most of the businesses of a modern society, and additionally have come to be important learning aids and tools in the home. Such computers include the large mainframe machines which process enormous amounts of data, large and small minicomputers that are now common in businesses and the home, and microcomputers which can be built into other devices for many purposes.
A common characteristic of all of these electronic computers is that they require electrical power to operate their various components, and in particular the usual approach is to provide power to the computer from the available main power line or source. As will be familiar to most persons, electrical power loss is occasionally experienced nearly everywhere, with varying degrees of frequency. For most appliances and machines powered by electricity, power outages are simply an inconvenience that temporarily halts operation, but does not result in any permanent loss or damage to the machine.
Electronic computers present a more complex problem when confronted with sudden and unexpected power losses. In a typical computer operation, data in the form of bits of information are retrieved from storage in memory, processed in a central processing unit, and the results of the processing are stored back in memory. Data or operating instructions may be retrieved from and stored to data files which are opened for access. Instructions in the form of keystrokes may be entered into the computer through a terminal. If the data or keystrokes should become lost or altered during the occurrence of a power loss, or if there is some alteration of the software operating environment as a result of the power loss, it may later be difficult or impossible to recover the information. Some types of potential losses and alterations are quite subtle in nature, and cannot be readily detected, making them even more serious problems because the computer user may obtain erroneous results with no warnings and no clue as to their cause. Thus, one of the greatest dangers during any unintended shutdown is that the computer will be shut down to an undefined or ill-defined state, from which an orderly startup to achieved a usable state is very difficult because the beginning state is unknown.
To cite a more concrete example, if "the plug is pulled" without any prior provision for orderly shutdown, the computer may be in the process of transmission of information to peripheral devices under operator instructions at the moment the failure occurs. The operator cannot be certain of how much of the information was transmitted successfully, and of whether electrical irregularities such as spikes during failure may have altered the information. The operator cannot conveniently reconstruct the failure to determine whether the information transmitted to the peripheral device is correct and reliable. The status of the computer is therefore poorly defined, and the operator cannot be certain what would happen if he simply restarted the computer in the hope that it would restart without losing information. The operator then can choose to gamble on an orderly restart, or begin the entire computing operation over, if that is possible under the circumstances.
Major power losses are relatively rare in most places. Unfortunately, computers are typically sensitive to brief power failures lasting only a fraction of a second and to partial power failures that reduce the main power line voltage below the design limits of the computer. The computer may be vulnerable to power losses and fluctuations that may not even be noticeable to a person who is watching the computer, and may not significantly affect many other types of electrical devices. Both major and minor power losses can interrupt normal computer operations in a way that makes reconstruction of the status and restoration nearly impossible, because it is difficult to determine the exact time, status, and failure sequence.
As a response to the extreme sensitivity of computer systems to electrical interruptions, uninterruptable power supplies have been developed for nearly all types of computers. Typically, an uninterruptible power supply includes a battery power source that is tapped when the main power is interrupted, to provide a continuous flow of electrical power to the computer. The DC power provided by the battery is converted to AC power for use by the computer in an inverter that is ordinarily part of the uninterruptable power supply. Standby generators are ordinarily not relied upon as the primary backup, since generators usually require at least several seconds from a cold start before reaching their rated power output. Battery backup power sources provide highly satisfactory service during short power interruptions, and most computers having such an uninterruptible power source operator continuously through such interruptions. Uninterruptible power sources are now available for large business computers and for the smaller minicomputers found as stand-alone units in businesses and homes.
It is not possible to predict beforehand whether a power interruption will be a few seconds or hours in length. Uninterruptable power sources are usually built to supply the power needs of the computer for a period of a few minutes, as for 20 minutes. If the power is lost for longer periods, the batterys of the uninterruptible power source become exhausted, and power to the computer is lost. The result is then the same as if there were no backup available in the first place. When such a longer duration power outage occurs, the computer operator may not be available to shut down the computer in an orderly fashion to avoid loss of information during the shutdown. Even when a computer operator is available, he may be relatively untutored as to the correct procedures for shutting the computer down in an orderly fashion, again without loss of information. On the other hand, the operator may be experienced and may be able to respond to the power loss in a fully acceptable manner that is appropriate for the particular operation then underway.
Another important concern is that, once the main power is restored, the computer must be able to resume operation, recognizing the fact that its then-current software environment is that existing when the interruption occurred due to the power failure. The computer operating system must first be "booted" into the computer, and then the operating program reloaded and restarted. If no operator is present, it would be desirable to have an automatic restart capability, so that valuable computing time is not lost until the operator returns. If an operator is present, either a fully manual start or a preprogrammed restart could be accomplished, again depending upon a decision of the operator.
At the present time, there is a need for a "smart" backup power system which can provide backup power to the computer when main power is interrupted, provide for continuation of computer operations during power outages of short duration and also for orderly shutdown of the computer during longer outages, and provide for the possibility of operator intervention as necessary. Such a system should allow orderly restart of the computer, either with or without operator intervention. Moreover, such a backup power system should be a stand-alone, plug in system that does not require hardware modifications to the computer itself, since the need for hardware modifications would deter many small business and home users of computers from using such a back up power system. The present invention fulfills this need and further provides related advantages.